These devices have means for balancing the weight of the suspended object and enabling the articulated rod system to be lengthened or shortened. These means currently consist (in the smaller types of systems) of one or two leaf springs that provide an approximately constant load independently of how much the system may be extended and that are spiral-wound. These springs have many drawbacks, including:
the risk of sudden breakage when the spring is under tension. This can cause very serious harm and permanent injury to anyone near the device; PA0 the difficulty of adjusting the load of the spring to suit the weight of the object hanging from the device. In order to make adjustments, the spring has to be dismantled from the articulated rod system; PA0 the articulated rod system contracts suddenly under the spring loading whenever the object it is supporting is removed.